The recent expanding scale of the computer network and the importance of security for data management have been increasing the demand for magnetic tape having an increased recording capacity for use as a medium for data backup. Approaches to high recording capacity are divided into improvement on recording density and extension of the tape length.
Since the tape length that can be put in a tape cartridge as wound is the upper limit of the recording capacity, extension of the tape length for increasing the recording capacity cannot be achieved but by reducing the tape thickness. Therefore, an increase in recording capacity attained by this approach is of necessity limited. With respect to the method of increasing a recording density, it is known that magnetic tape has a lower recording density than a hard disc drive. Serpentine type magnetic tape particularly has a low recording density, which is due to the low track density. On the other hand helical scan type magnetic tape is known to have a higher track density than the serpentine type magnetic tape. This is because the magnetic tape of helical scan type uses a servo tracking system called automatic track finding (ATF).
A servo tracking system has also been adopted to serpentine type magnetic tape to improve the track density. Methods that have been proposed as such a servo tracking system include an embedded servo system, in which servo signals are written on the same track as the data track on the magnetic recording surface, and a system in which a track exclusive to servo signals is provided on the magnetic recording surface. Japanese Patent Publication No. 82626/95 proposes a tracking system particularly useful where the pitch of data tracks is as small as several tens of microns, in which a dedicated track for servo information is provided on the magnetic recording surface, and a plurality of servo signal reproduction heads are used to read the servo signals for tracking. According to this technique, however, the number of servo signal reproduction heads must be increased as the number of tracks increases. In order to avoid this, the servo track should be increased. Like this, conventional servo tracking systems use the same side of magnetic tape as used for data recording, which results in reduction of the data recording area. This problem is conspicuous in the servo tracking system of Japanese Patent Publn. No. 82626/95 when a track density is as high as about 30 tpmm (tracks per mm) or even more.